New assays for the function of receptors for complement fragments and for immunoglobulin on the fixed phagocytic cells of the reticuloendothelial system have been developed. The assays examine the clearance of erythrocytes with immunologically active molecules on their surface from the circulation of patients and controls. The first studies demonstrated a defect in the function of C3b receptors in patients with primary biliary cirrhosis. This defect is not present in patients with chronic active hepatitis or alcoholic cirrhosis. More recent studies defined a profound defect in Fc receptor function in patients with systemic lupus erythematosus, which is directly related to the presence of circulating immune complexes. This defect is, in turn, closely related to the patient's disease activity. BIBLIOGRAPHIC REFERENCES: Jaffe, C. J., Atkinson, J. A., and Frank, M. M: The role of complement in the clearance of cold agglutinin sensitized erythrocytes in man. J. Clin. Invest. 58: 942-929, 1976. Frank, M. M.: The effect of IgM and IgG complement fixing antibodies and of complement on erythrocyte survival. In Pollack, W., Mollison, P. L., and Reiss, A. M. (Eds.): An International Symposium on the Nature and Significance of Complement Activation. 1977, pp. 13-27.